A. Technical Field
The present invention relates generally to camera systems, and more particularly, to efficiently determining focus and exposure settings for a camera system acquiring a photograph of a frame within a multi-frame source image.
B. Background of the Invention
Consistent high-quality image acquisition is oftentimes a challenging task for many camera systems. The resolution requirements of these camera systems may change from application to application. For example, a microscopic resolution of a semiconductor substrate may be required to allow an analysis of the manufactured pattern thereon. Obtaining a full image of the substrate at a microscopic resolution is difficult because of the size of the substrate, the resolution requirements of the image and inclination of the substrate with respect to the camera.
High-resolution cameras are commonly used to generate images of microscopic resolution. The field of view of a high-resolution camera is typically relatively small resulting in the camera being unable to bring the entire substrate within its field of view. In such instances, a high-resolution image of a substrate may be obtained by partitioning the substrate into multiple frames and taking a photograph of each frame. Once all of the frames have been photographed, all of the frame images are combined or stitched together to provide a single image of the substrate. However, maintaining sufficient image quality across each of the frames is frequently difficult to achieve because of variations between each of the frames.
FIG. 1 illustrates an exemplary source image, such as a pattern manufactured on a semiconductor substrate, which is divided into multiple frames or segments. As shown, the source image 110 is divided into equal frames including Segment (1) 120, Segment (2) 130 through Segment (N) 140. Although FIG. 1 shows the frames as having the same shape and area, it may be the case that the source image 110 is divided into unequal frames. Additionally, some or all of the segments may have overlap which all for improvements in the subsequent combination or stitching of the segments into a photograph of the source image 110.
As a camera is moved from one frame to another frame, the quality of the images may degrade. This degradation may result from inconsistent light from one frame to another. In addition, the surface of the pattern or substrate may not be completely smooth resulting in variations in the distance between the pattern surface and the camera. Further yet, the pattern densities and designs may be substantially different from one frame to another which may also affect the quality between the frame images.
The quality of each frame image may be characterized using various different parameters. For example, the quality of a frame may be measured using both contrast and sharpness indicators. One factor that defines the contrast of an image is the exposure setting on the camera. If the exposure setting is not optimized, then the image contrast will likely be over lower quality. One factor that defines the sharpness of the image is the focus setting on the camera. If the focus setting is not optimized, then the image sharpness will appear blurry and the edges within the image will not be defined.
The importance of generating consistently high-quality images is well understood when the images are to be stitched or combined together. If certain frame images are out of focus or have poor contrast, then the stitched image may appear awkward and difficult to analyze. Because a large multi-frame image may require a large number of frame images to be taken, the process of optimizing the camera may be tedious and time consuming.